Dithering systems have been used in a number of technologies in the past. The objective of a dithering system is to change a characteristic of a particular signal in a periodic (or random) fashion in order to provide a useful output. As is described in further detail, the dithering system of the invention may be used to change the relative location of an optical signal.
In an exemplary liquid crystal display sometimes referred to as an image source, there usually are a plurality of picture elements, sometimes referred to as pixels or pels, and these pixels can be selectively operated to produce a visual output in the form of a picture, alphanumeric information, etc. Various techniques are used to provide signals to the pixels. One technique is to use a common electrode on one plate of a liquid crystal cell which forms the display and an active matrix electrode array, such as that formed by thin film transistors (TFT), on the other plate of the liquid crystal cell. Various techniques are used to provide electrical signals to the TFT array to cause a particular type of optical output from respective pixels.
One factor in determining resolution of a liquid crystal display is the number of pixels per unit area of the liquid crystal display. For example, Sony Corporation recently announced a 1.35 inch diagonal high resolution liquid crystal display which has 513,000 pixels arranged in 480 rows of 1,068 pixels per row.
Another factor affecting resolution is the space between adjacent pixels sometimes referred to "as optical dead space". Such space ordinarily is not useful to produce an optical signal output. The space usually is provided to afford a separation between the adjacent pixels to avoid electrical communication between them. The space also is provided to accommodate circuitry, leads, and various electrical components, such as capacitors, resistors, and even transistors or parts of transistors.
There is a continuing need and/or desire to improve resolution of displays. It also would be desirable to facilitate the placing of circuitry in a display while minimizing the optical dead space caused by the circuitry.
The present invention may be used with various types of displays and systems. Exemplary displays are a CRT (cathode my tube) display, a transmissive liquid crystal display that modulates light transmitted therethrough, reflective liquid crystal displays, light emitting displays, such as electroluminescent displays, and so on.
Conventional optical displays typically display graphic visual information, such as computer generated graphics, and pictures generated from video signals, such as from a VCR, from a broadcast television signal, etc.; the pictures may be static or still or they may be moving pictures, as in a movie or in a cartoon, for example. The visual information also may be of the alphanumeric type in which numbers, letters, words, and/or other symbols (whether in the English language or in some other language) are presented for view. Visual information viewed by a person (or by a machine or detector) usually is in the form of visible light. Such visible light is referred to as a light signal or an optical signal. The term optical signal with which the invention may be used includes visible light, infrared light, and ultraviolet light, the latter two sometimes being referred to as electromagnetic radiation rather than light. The optical signal may be in the form of a single light ray, a light beam made up of a plurality of light rays, a light signal such as a logic one or a logic zero signal used in an optical computer, for example, or the above-mentioned alphanumeric or graphics type display. Thus, as the invention is described herein, it is useful with optical signals of various types used for various purposes. Therefore, in the present invention reference to optical signal, light ray, light beam, light signal, visual information, etc., may be used generally equivalently and interchangeably.
The picture elements (pixels or pels) mentioned above may be discrete pixels, blocks or areas where an optical signal can be developed by emission, reflection, transmission, etc. such as the numerous pixels in the miniature image source of Sony Corporation mentioned above. The optical signal referred to may mean that light is "on" or provided as an output from the device, or that the pixel has its other condition of not producing or providing a light output, e.g., "off"; and the optical signal also may be various brightnesses of light or shades of gray. Alternatively, the optical output or optical signal produced by a pixel may be a color or light of a particular color.
The pixels may be a plurality of blocks arranged in a number of lines or may be a number of blocks randomly located or grouped in a pattern on the display or image source (source of the optical signal). The pixels may be a number of lines or locations along the raster lines that are scanned in a CRT type device or the pixels may be one or a group of phosphor dots or the like at particular locations, such as along a line in a CRT or other device.
The optical signal produced by one or more pixels may be the delivery of light from that pixel or the non-delivery of light from that pixel, or various brightnesses or shades of gray. To obtain operation of a pixel, as is described herein, for example, the pixel may be energized or not. In some devices energizing the pixel may cause the pixel to provide a light output, and in other devices the nonenergizing of the pixel may cause the providing of a light output; and the other energized condition may cause the opposite light output condition. It also is possible that the nature of the light output may be dependent on the degree of energization of a pixel, such as by providing the pixel with a relatively low voltage or relatively high voltage to obtain respective optical output signals (on and off or off and on, respectively).
For example, in a conventional twisted nematic liquid crystal display device, polarized light is received by a liquid crystal cell, and depending on whether the liquid crystal cell receives or does not receive a satisfactory voltage input, the plane of polarization of the light output by the liquid crystal cell will or will not be rotated; and depending on that rotation (or not) and the relative alignment of an output analyzer, light will be transmitted or not. In an optical phase retardation device that has variable birefringence, such as those disclosed in U.S. Pat. Nos. 4,385,806, 4,540,243, and Re. 32,521 (sometimes referred to as surface mode liquid crystal cells), depending on the optical phase retardation provided by the liquid crystal cell, plane polarized light may be rotated, and the optical output can be determined as a function of the direction of the plane of polarization.